1. Field of the Invention
The present invention relates to a still picture picturephone communication system, and in particular, to an improvement in a still picture picturephone transmission system wherein a picture signal of a still picture obtained by picking up with a camera is modulated to a voice band signal and sent out to a telephone circuit, and wherein a picture signal supplied through the telephone circuit is demodulated to be visualized on a display.
2. Description of the Prior Art
A picturephone which sends voice and picture simultaneously by using a telephone communication circuit has been considered desirable. Practically, however, it is difficult to continuously transmit and receive a dynamic picture which requires a great amount of data through telephone communication circuits presently used. Thus, a still picture picturephone for transmitting a still picture to the called party during talking is used instead.
In this still picture picturephone, it is possible, during talking with normal voice, to send a desired still picture, for example, a face of the talking person, a photographic picture plane or drawings corresponding to the contents of the talking arbitrarily by interrupting the talking temporarily.
Accordingly, the advantage has been provided in the still picture picturephone mentioned above in that a picture can be sent and received over a telephone circuit which was impossible heretofore, and that since only one still picture is sent each time when required, the amount of data processing is limited, thereby to make it easy to put the picturephone to practical use.
Hereinafter, a still picture picturephone set using a prior art still picture picturephone communication system will be described with reference to the drawings.
FIG. 1 shows a circuit diagram of a still picture picturephone set disclosed, for example, in "Foreign Communications Technique", the October number, 1986.
In the Figure, reference numeral 1 designates a handset, 2 a microphone, 3 a voice input/output circuit, 4 an analog circuit, 5 a matrix switch, 6 a telephone interface circuit, 7 a telephone circuit connection terminal, 8 a speaker, 9 a key pad, 10 an input/output port, 11 a CPU, 12 a program memory, 13 a modulator and demodulator (MODEM) circuit, 14 a TV camera, 15 an image controller, 16 an image memory, and 17 a display. On the other hand, FIG. 2 shows a sequence diagram of a picture transmission procedure for the above picturephone set.
Next, the operation for the transmission of voice and a picture signal in the prior art picturephone set will be described with reference to FIGS. 1 and 2. In FIG. 1, a call with voice is sent to the telephone circuit connection terminal 7 from the handset 1 or microphone 2 through the voice input/output circuit 3, analog circuit 4, matrix circuit 5, and telephone interface circuit 6. Further, a voice signal from the called party is transferred to the handset 1 or speaker 8 through a reverse route of the above-mentioned signal route, and it is reproduced by the handset 1 or speaker 8.
On the other hand, in transmitting the picture signal, as shown in FIG. 2, handshaking is carried out and then the still picture transmission is performed.
Specifically, in order to ascertain whether the picturephone set of the called party is of the same type, header frame comprising an identification code data (hereinafter referred to as ID code) indicating the capability of equipment is sent out, and after the sent back ID code from the called party is ascertained, the picture data is transmitted. The header frame comprises frame synchronizing data for synchronization, preamble data and signal for auto gain control and amplitude regulation and each is set before ID code (not shown).
Here, in FIG. 3(a), the components of the header frame are shown, and in FIG. 3(c), an ID code at the time of picture data transmission is shown.
As shown in FIG. 3(b), the ID code at the time of handshaking consists of 0 data of the first 8 bits, machine data (M) indicating the function of the picturephone set, frame classification data (F) indicating the frame classification such as the number of pixels in a frame to be transmitted, ID extension code data indicating the continuation of ID codes, and frame check sequence data (FCS). Furthermore, in the ID code at the time of picture data transmission, as shown in FIG. 3(c), length data (L) indicating data quantity per one line is formed in the first 8 bits, and frame classification data (F) indicates a frame classification of picture data to be transmitted actually to achieve matching of functions of both equipments which perform transmission and reception respectively. The data arrangement within both ID codes is identical.
Thus, in FIG. 1, when the sending out of a picture is instructed by the key pad 9, the CPU 11 detects this through the input/output port 10, and ID code is sent out to the modulator and demodulator (MODEM) 13 in accordance with a program stored beforehand in the program memory 12. After this ID code is modulated to an analog signal, it is sent out through the matrix switch 5 from the telephone circuit connection terminal 7.
The ID code from the called party is transferred to the CPU 11 through a reverse route of the above signal route, and the CPU 11 ascertains the ID code. During this time period, the image picked up by the TV camera 14 is quantized in the image controller 15 and stored in the image memory 16. The stored data is sequentially led out and displayed on the display 17, and it is also outputted to the telephone circuit connection terminal 7 from the image memory 16 according to a command of the CPU 11.
Furthermore, when an ID code or image data is inputted from the called party, the matrix switch 5 changes over the destination of a received signal through the telephone interface circuit 6 in accordance with a received carrier signal such that the analog circuit 4 is changed to the modulator and demodulator circuit 13.
After the received signal has been demodulated in the modulator and demodulator circuit 13, the CPU 11 returns or stores the ID code in the image memory 16, and the image controller 15 sequentially picks up the image data of the calling party and the image data of the called party for display on the display 17.
When the transmission and reception of the picture have been finished and no carrier signal is supplied from the modulator and demodulator circuit 13, the matrix switch 5 connects the telephone interface circuit 6 to the analog circuit 4 thereby to restore the talking with voice.
In the prior art, as shown in FIG. 2, the response to the ID code, or the sending out of the picture data was carried out after waiting one second from the reception of the ID code of the other party.
Specifically, in the prior art picturephone set, it is arranged to perform the matching of impedance between the circuit and the picturephone set when the picture send-out instruction is inputted. As a result, in order to achieve the data reception correctly, one second is necessary as a response waiting time, and the response was delayed one second automatically
In the prior art still picture picturephone communication system, since it is arranged as described above, the problem is that one second of waiting time is not necessary when the transmission is carried out to equipment with which no impedance matching is required.
Furthermore, in the prior art communication system, in order to ascertain whether the picturephone telephone sets at both ends are of the same system classification, as described above, a header including an ID code is sent out by handshaking. Furthermore, at the receiving party, the ID code sent thereto is ascertained, and then an ID code indicating the system classification of the receiving end is sent back. In this case, the above-mentioned system classification indicates, for example, the capability of the telephone sets of the sending and receiving parties, that is, the size of the screens (picture planes) in terms of a number of pixels at the sending and receiving ends, and the screens are classified into a number of classifications including 48.times.48, 64.times.64, 96.times.96, 128.times.128 pixels, etc.
Accordingly, when the pixel numbers differ from each other at the sending and receiving ends, a situation will be encountered in which still picture data obtained by complex operations can not be sent to the receiving party. Thus, in the prior art system, before sending and receiving picture data, it has been necessary to perform the handshaking by sending out and actually sending back the headers including the ID codes.
Consequently, the prior art system involves the drawback in that a considerable time is required for the handshaking, and the interruption time of the talking becomes long.
On the other hand, the picture data in the prior art example mentioned above is modulated to a picture signal in the following manner. In other words, in the example shown in FIG. 4, the modulated signal is made of phases, including first phase of a sine curve type and a second phase of an inverse sine curve type which are out of phase by 180 degrees, and each phase is formed with a plurality of signals of different amplitudes. These one-cycle signals of particular phases and particular amplitudes are made to correspond to particular colors. In this example, each phase includes eight cycles, and thus, a total of sixteen cycles are included in the two phases. A signal "15" having the maximum amplitude in the first phase corresponds to white, a signal "0" having the maximum amplitude in the second phase corresponds to black. Intermediate signals "14".about."1" correspond respectively to gray of different lightness.
In such a prior art still picture picturephone communication system, it is possible to perform talking with voice, and the transmission and reception of a still picture at a suitable timing. However, the function for transmitting and receiving character data including character information and the like has not been provided. As a result, there has been a problem in that in order to transmit and receive the character data, a separate, independent and large apparatus is necessary.
Furthermore, in the prior art still picture picturephone mentioned above, the images picked up by the built-in cameras of the respective parties are merely sent and received in accordance with transmission commands by both parties. As a result, there is a problem that when a talking person is absent, it is impossible to transmit the picture data.
Moreover, in the prior art still picture picturephone mentioned above, it is possible to demodulate the picture data sent from the other party in communication and to display the same on a display. The picture data sent from the other party is stored in an image memory. However, it has been impossible to transfer the picture data stored in the image memory to a third party.